Published on Web 10/28/2009
Wavelength-Selective Photoactivatable Protecting Groups for
Thiols
Nico Kotzur, Benoˆıt Briand, Michael Beyermann, and Volker Hagen*
Leibniz-Institut fu¨r Molekulare Pharmakologie (FMP), Robert-Ro¨ssle-Strasse 10,
13125 Berlin, Germany
Received August 28, 2009; E-mail: hagen@fmp-berlin.de
Abstract: We developed and characterized efficient, remarkably water-soluble photolabile protecting
groups for thiols based on 2-nitrobenzyl and (coumarin-4-yl)methyl chromophores, among them two
new ones. The protecting groups allow, due to their different absorption maxima, wavelength-selective
photocleavage of binary mixtures of cysteine derivatives protected at the thiol function with various
photolabile protecting groups by irradiation with light. The concept was also functional with the two
different S-protected cysteine residues in derivatives of the model peptide resact. Selective photolysis
could be achieved for the peptides Ac0-Cys1(BCMACMOC),Cys8(7,8BCMCMOC)-resact and Ac0-
Cys1(C4MNB),Cys8(BCMACMOC)-resact by irradiation with light of g402 nm or g436 nm wavelength,
respectively, followed by irradiation at λ g 325 nm.
zyl,4 phenacyl,5 benzoinyl,6 or coumarinyl7 protecting groups.
However, most of the reported protecting groups have water
Introduction
Photolabile protecting groups are well established in various
fields of chemistry and biology.1 In particular, the liberation of
biomolecules from biologically inactive, light-sensitive precur-
sors (caged compounds) is a powerful tool in biochemistry for
which numerous applications have been described.2 Further-
more, the concept of chromatic orthogonality, that is the
possibility of selectively removing one protecting group in the
presence of others in any chronological sequence by irradiation
with light, is an interesting aspect that could be extended to
selective processes.3 To our knowledge, this has not been applied
to biomolecules as yet.
solubility problems. Therefore, they are not well suited for our
intended application. Herein, we report different photolabile thiol
protecting groups based on (coumarin-4-yl)methyl and 2-ni-
trobenzyl scaffolds which are remarkably hydrophilic and
sensitive to irradiation at specific wavelengths. We present their
synthesis and photochemical properties and demonstrate the
effective wavelength-controlled photocleavage of various S-
protected N-Fmoc-cysteine mixtures and of S-protected deriva-
tives of the model peptide resact.
Results and Discussion
In peptide chemistry, cysteines play a crucial role in native
chemical ligation and formation of disulfide bridges. For
investigations of peptide folding, selectively cleavable thiol
protecting groups, which require only light and no addition of
reagents, would be very useful. Because these studies are
performed in aqueous buffer solutions, the protecting groups
should not diminish the solubility and therefore have to be
hydrophilic. To explore the applicability of photolabile protect-
ing groups in this respect, we looked for appropriate thiol
protecting groups, which allow wavelength-controlled photolysis
of S-protected cysteines. Examples developed for the efficient
photolysis of protected thiol functions are based on 2-nitroben-
Synthesis and Properties of S-Protected Fmoc-Cys-OH
Derivatives. For the photolabile S-protection of Fmoc-Cys-
OH derivatives, we explored differently substituted (cou-
marin-4-yl)methoxycarbonyl (CMOC) and 2-nitrobenzyl
(NB) scaffolds. The syntheses of the corresponding S-
protected Fmoc-Cys-OH derivatives 1-4 are shown in
Scheme 1. Carboxylate functions introduced at nonconju-
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10.1021/ja907287n CCC: $40.75 2009 American Chemical Society
J. AM. CHEM. SOC. 2009, 131, 16927–16931 16927